1. Field of the Invention
The present invention relates to an oscillator module, such as a voltage controlled oscillator for use in a communication apparatus, in particular, in a mobile communication apparatus.
2. Description of the Related Art
As an example of a known oscillator module, a voltage controlled oscillator is described below with reference to the drawings.
Referring to FIGS. 7 through 9, a voltage controlled oscillator 20 includes a multi-layered base 1. The multi-layered base 1 is formed by laminating a plurality of glass epoxy substrates on which circuit patterns 2 (only partially shown) are disposed, which is described later. The circuit patterns 2 are formed on one main surface (obverse surface) and the inside of the multi-layered base 1. Mounted on one main surface of the multi-layered base 1 are electronic components 3, such as a chip capacitor, a chip resistor, and a transistor. Through-holes 4 are formed on lateral surfaces of the multi-layered base 1. The through-holes 4 are used as external terminals, and through-holes electrodes 5 are formed on the surfaces of the through-holes 4.
The through-hole electrodes 5 and the circuit patterns 2 are electrically connected via through-hole forming portions disposed on one main surface or the inside of the multi-layered base 1.
Formed on the other main surface (reverse surface) of the multi-layered base 1 are, as illustrated in FIG. 9, reverse electrodes 6 and 7, both of which are electrically connected to the through-hole electrodes 5 formed on the surfaces of the through-holes 4. The reverse electrode 6 serves as a ground electrode, while the reverse electrodes 7 serve as terminal electrodes.
Referring to FIG. 8, a shield cover 8 is placed to cover one main surface of the multi-layered base 1. A voltage controlled oscillator 20 is thus formed. The shield cover 8 is provided with notches 8a so as not to contact the circuit patterns 2. A manufacturing process for the voltage controlled oscillator 20 constructed as described above is now described with reference to FIGS. 10 and 11.
A mother base 9 is first prepared by laminating and firing a plurality of ceramic green sheets provided with circuit patterns 2 (only partially shown). Through-holes 4 are then formed on split lines S that divide the mother base 9, and electronic components 3 are mounted on one main surface of the mother base 9. Through-hole electrodes 5 are formed on the inner surfaces of the through-holes 4 by means such as plating. Thereafter, the mother base 9 is diced along the split lines S with a dicer, thereby obtaining a plurality of individual bases 10 on which the electronic components 3 are mounted.
After characteristic adjustments, such as frequency adjustment, are made on each base 10, a shield cover 8 is placed, as illustrated in FIG. 11, to cover one main surface of the base 10. A voltage controlled oscillator 20 is thus formed.
The voltage controlled oscillator 20 is then placed on a mounting board 11, and the through-hole electrodes 5 are connected to wiring patterns 12 on the mounting board 11 with the use of solder 13. Thus, the voltage controlled oscillator 20 is mounted on the board 11.
However, the above known type of voltage controlled oscillator presents the following problems.
Since the through-holes 4 are used as external terminals, the area of the multi-layered base 1 is increased by an amount equal to the size of the through-holes 4, thereby enlarging the overall voltage controlled oscillator 20.
In mounting the voltage controlled oscillator 20 on the board 11, the solder 13 for connecting the voltage controlled oscillator 20 with the board 11 is formed in a fillet-like shape, thereby projecting outwardly from the bottom surface of the multi-layered base 1. Accordingly, the area where the voltage controlled oscillator 20 is mounted on the board 11 is increased.
When the voltage controlled oscillator 20 is used in a mobile communication apparatus, interference disadvantageously occurs between the voltage controlled oscillator 20 and a power amplifier within the communication apparatus. More specifically, a high output of the power amplifier interferes with the voltage controlled oscillator 20 so as to slightly modulate the frequency range used in the oscillator 20, thereby degrading sound quality of the communication apparatus. This is due to the following reason. Notches 8a are provided for the shield cover 8 to avoid an electrical connection between the shield cover 8 and the circuit patterns 2. Because of the provision of the notches 8a and the exposed through-holes 4, which serve as external terminals, the voltage controlled oscillator 20 cannot be completely shielded from an external source and is thus externally influenced by unwanted radiation.
Hitherto, the split lines S of the mother base 9 are arranged along the through-holes 4. Since the mother base 9 is split along the split lines S, burrs are generated at the end portions of the through-holes 4 of the obtained individual bases 10, or the through-hole electrodes 5 formed on the surfaces of the through-holes 4 come off. Consequently, the uniformity of the flatness of the voltage controlled oscillator 20 is impaired, thus making it difficult to mount the voltage controlled oscillator 20 on the board 11. Additionally, the through-hole electrodes 5, which serve as external terminals, come off, thereby reducing the reliability of the adhesion between the oscillator 20 and the mounting board 11.
Hitherto, various characteristics, such as frequency characteristics, are adjusted after the mother base 9 is divided into the individual bases 10. This is because of the following reason. In the mother base 9, the through-hole 4, which serves as an external electrode, is shared between adjacent bases 10. If characteristics are checked on the individual bases 10 when they are still connected, one base 10 is influenced by another base 10 whose characteristics have not yet been checked, thereby failing to correctly make characteristic adjustments. It is thus necessary to check characteristics of each base 10 after the mother base 9 is divided. However, this is very time-consuming and troublesome, thereby giving rise to an increase in the cost.